A wall-jet flow cell was used to study O2 reduction at AA2024-T3. In buffered O2-saturated solution the current density was 2% of the diffusion-limited value and relatively stable with time. In unbuffered solution the current density was 25-50% of the diffusion-limited value. The higher currents under unbuffered conditions are attributed to production of OH- via O2 reduction at the intermetallic particles (IPs) at AA2024-T3. Trenching was observed around both Cu-rich and Fe-rich IPs. This cathodic corrosion was observed in the absence of chloride and when the alloy was held potentiostatically at open-circuit potential demonstrating that both types of IPs can act as cathodes toward O2 reduction under these conditions.